Scraped removal of metal oxide deposit by a ceramic edge



Jan. 21, 1969 n. E. DARR ET A1. 3,423,186

SCRAPED REMOVAL OF METAL OXIDE DEPOSIT BY A CERAMI'C EDGE Sheet Filed July 2, 1964 am mmmmm c. Timun va WD5/w@ vm em@ m mww# n Oma A Fer. W V1 B. AI .In Il G 2. n

Jan. 21, 1969 D. E. DARR ET AL 3,423,186

SCRAPED REMOVAL OF METAL OXIDE DEPOSIT BY A CERAMIC EDGE Sheet Filed July 2, 1964 Hlm FIG. 6

INVENTOR. DONALD 6. mee. ,eacfe s. HSL-' 1% Mew/ETH w. 21a/mensa Arme/vsn' i f MU Jan. 21, 1969 D. E. DARR ET AL I 3,423,186

SCRAPED REMOVAL OF METAL OXIDE DEPOSIT BY A CERAMIC EDGE Filed July 2, 1964 Sheet 3 of 4 Avon/Irvs' H64 ,i mwwk Jan- 21, 1969 D. E. DARR ET A1.

SCRAPED REMOVAL OF METAL OXIDE DEPOSIT BY A CERAMIC EDGE Sheet Filed July 2, 1964L INVENTORS DONALD 5. DER. EOGEB S. LE/SER.

BY cL/Ffozo E. Loana M KNIIGTH W. /CIMBDSON ATI-crever.:

United States Patent O 3,423,186 SCRAPED REMGVAL F METAL OXIDE DEPOSIT BY A CERAMIC EDGE Donald E. Dari', Wadsworth, Ohio, Roger S. Leiser, De-

catur, Ill., and Clifford E. Loehr, Akron, and Kenneth W. Richardson, Barberton, Ohio, assignors to PPG Industries, Inc., a corporation of Pennsylvania Filed July 2, 1964, Ser. No. 379,825 U.S. Cl. 23-293 15 Claims Int. Cl. B08b 1/04; B01j 1/00 ABSTRACT OF THE DISCLOSURE In the production of metal oxides, e.g., by vapor phase oxidation of metal halide, deposits of metal oxide are formed on the walls of the reaction chamber. The metal oxide is removed by scraping it oifthe surface with a solid cera-mic edge highly resistant to corrosive environment, of relatively low thermal conductivity and of a minimum predetermined hardness.

This invention relates to a novel method and apparatus to be used in conjunction with the oxidation of a metal halide to produce metal oxide. More particularly, it relates to a method and apparatus to be used in the production of titanium oxide by the vapor phase oxidation of titanium tetrahalide, c g., TiCl4, TiBr4, and TiI4.

In the typical vapor phase oxidation process for the production of titanium dioxide, titanium tetrahalide and an oxygenating gas, eg., oxygen or oxygen-containing gas, are introduced into a closed reaction chamber either in the presence or absence of a iluidized bed, the chamber preferably maintained at a temperature above 600 C. in a range of about 850 to 1,700" C. Typical processes are disclosed in U.S. Letters Patents 2,653,078 to Lane; 2,- 750,260 to Nelson et al.; 2,791,490 to Willcox; 2,670,275 to Olson et al.; 2,823,982 to Saladin et al.; 2,968,529 to Wilson; 2,989,509 to Frey; 3,068,113 to Strain et al.; 3,069,281 to Wilson and 3,069,282 to Allen.

The metal halide, e.g., titanium tetrachloride, is preferably introduced into the reaction chamber or reactor in a vapor state and is oxidized by oxygen or oxygen-containing gas such that titanium dioxide is formed.

The walls of the oxidation reaction chamber are preferably constructed out of a zirconium base brick, ceramic, or other suitable material. A frequent problem encountered in the production of titanium dioxide is the formation of a metal oxide growth or encrustation upon the walls of the reaction chamber. If this encrustation or metal oxide formation and buildup is not timely removed, it develops into a donut or ring which eventually closes up and plugs the reactor, thereby hindering the continuous and economical operation of a T102 vapor phase oxidation process and making the process impractical as a commercial operation.

In the prior art, several methods have been -proposed for removing the metal oxide accumulation. Thus, it has been proposed to flow a gas transversely through the reactor walls. See `for example, U.S. Letters Patent 2,957,- 753. U.S. Letters Patent 2,805,921 issued to Schaumann (also note British Specification 822,910) teaches the dislodging of the scale by means of an internally cooled cutting element. The reactor walls also may be cleaned via sonic vibrators. It has also been taught that oxide scale build-up may be prevented by diffusion of inert gases through porous metal Walls. Belgium Patent 640,553 teaches the flexing of the reactor walls as a means of removing oxide growth.

In the practice of the present invention, the metal ox ide scale buildup is continuously removed and further buildup prevented by passing one or more solid ceramic Patented Jan. 21, 1969 or lava edges immediately adjacent to the surface of the reactor wall, such that each solid ceramic edge brushingly contacts and displaces the metal oxide accumulation.

In one embodiment, the solid Ceramic edges are arranged in a circular or ring-like fashion about the reactor axis and moved to and fro, that is, recipocated upwardly and downwardly, in a direction parallel to the reactor axis.

In a preferred embodiment the ceramic edges are positioned as arms or strips parallel to the reactor axis and moved in a circumferential direction along the reactor `wall about the axis.

Likewise in the preferred practice of this invention, it is preferred that the solid Iceramic dedusting members or edges be supported and retained in the predetermined position iby means of support members thereby increasing the overall section modulus. Such support members are particularly desirable where one or more ceramic arms are projected upwardly from the bottom of the reactor in cantilever fashion along the reactor walls, that is, in a direction parallel to the reactor axis.

Although the supports may be constructed out of ceramic material, it is preferred to employ a material that will :provide high strength per pound particularly at the elevated temperature conditions within the reactor. It has been found that a suitable lmaterial is nickel formed or shaped as tubular or pipe-like elements `and through which lthere is circulated a `cooling, heat transfer fluid.

Although the supports may be constructed out of a metal material as noted above, it is essential that the brushing or dedusting Iarms be constructed out of ceramic since metallic materials abrade and quickly wear away, particularly at the edge such that there results a flattened edge which tends to compact the metal oxide onto the wall surface rather than remove it. However, when ceramic is employed, the solid edge member retains its shape and thus continues to perform its brushing and dedusting functionover a prolonged period.

The invention will be better understood by reference to the drawings and the gures thereon;

FIGURE l represent a 3-dimensional view of one preferred embodiment of the present invention.

FIGUR-E 2 represents a cross-section through FIGURE 1 through a plane just below the caps 7, 7A, rand 7B, parallel to the reactor bottom 12.

FIGURE 3 represents a modification of FIGURE l wherein only one ceramic deduster arm is employed.

FIGURE 4 represents a 3-dimensional view of a further practice of the present invention.

FIGURE 5 is a plan view of FIGURE 4.

FIGURE 6 represents a 3-dimensional view of a ceramic dedusting arm.

FIGURE 7 represents a plan view of FIGURE 6.

FIGURE 8 represents a plan view of a modication in the geometric shape of the ceramic dedusting arm.

FIGURES 9 :and 10 represent cross-sectional views of various reactor shapes and also show schematically the positioning of `a ceramic arm within each reactor.

FIGURE 1l represents a top portion of a reactor with 1a` concentric tube arrangement by which reactants are introduced.

FIGURE 1 represents an overall 3dimensional view of one preferred embodiment of the present invention. FIG- URE 2 is a plan view of FIGURE 1.

More particularly, there is shown in part a cylindrical metal oxide reactor wall 13 and a bottom 12 with :axial shaft 2 and concentric conduits 1 and 11 projecting upwardly through the center of bottom 12.

A cooling fluid is introduced from a source (not shown) into inlet conduit 1 and is flowed upwardly abou-t the shaft 2. At or near the top of conduit 1, the fluid stream splits and ows into support conduits 3, 4, 5, 3A, 4A, 5A, 3B,

4B, and 5B, each of which is connected to and projects from conduit 1 at an angle, e.g., 90, and then curves upwardly, e.g., by means of an elbow in a direction substantially parallel t the projected common axis of the shaft and conduits 1 and 11.

Ceramic dedusting arm 6 is held and maintained in a predetermined position in between support conduits 4 and 5 as shown. Similarly, each pair of support conduits 4A and 5A, 4B fand 5B, retains and supports respectively a ceramic dedusting arm 6A and 6B as shown in FIG- URE 2.

In addition support conduits 3, 4, and 5 support and retain center return conduit 8 in a predetermined position. Similarly conduits 3A, 4A, and 5A retain return conduit 8A and conduits 3B, 4B, and 5B retain return conduit 8B. Return conduits 8, 8A, 8B are preferably flattened to an elliptical shape as shown in the FIGURES 1 and 2. Tubes 3, 4, 5, 31A, 4A, 5A, 3B, 4B, and 5B also may be flattened to an elliptical shape.

At the top of center return conduit 8 there is affixed a cap 7 which provides a common closed chamber for conduits 3, 4, 5, and 8. Similarly cap 7A is aflixed to conduits 8A ,and cap 7B -is aflixed to conduit 8B thereby providing common chambers respectively for conduits 3A, 4A, 5A, 8A, and 3B, 4B, 5B, and 8B.

Internally of each conduit 8, 8A, and 8B there is provided respectively baflle means 9, 9A, and 9B.

Conduit 8 is then joined by connecting conduit 10 to conduit 8B, the conduit 10 being connected and joined to conduit 8 at a point above baille 9 and to conduit 8B at a point below baille 9B.

Similarly, conduit 8B is connceted to 8A by means of 10B which joins 8B at a point above 9B and 8A at a point below 9A.

Finally conduit 8A is connected to 8 by 10A which connects 8A lat a point above baffle 9A and 8 at a point below baille 9.

Thus, in the operation of the novel dedusting apparatus herenbefore described, a cooling iluid ilo-ws into and upwardly through conduits 3, 4, 5, 3A, 4A, 5A, 3B, 4B, and 5B The iluid ilows out of the upward ends of conduits 3, 4, and 5 into the chamber provided by cap 7 and then downwardly through center return conduit 8 to baflle 9, land then through connecting conduit 10 to return conduit 8A (at a point below baille 9B). The fluid then continues its llow downwardly in conduit 8B to exit conduit 11 which is connected to an appropriate reservoir (not shown).

Simultaneosuly fluid in conduit tubes 3B, 4B, and 5B flows into the chamber of cap` 7B, downwardly through center conduit 8B to baille 9B, through connecting tube 10B to center conduit 8A (below baffle 9A) and downwardly into conduit 11.

Likewise, iluid in conduit tubes 3A, 4A, 5A ilows into the chamber of cap 7A, downwardly through center conduit 8A to baille 9A, through connecting tube 10A to center conduit 8, and downwardly in tube 8 to conduit 11.

Simultaneously the entire assembly is rotated by shaft 2 -which is connected to tany appropriate or conventional drive means (not shown), and as the assembly turns, the ceramic scraping arms or elements contact and brush accumulated metal oxide from the reactor wall 13. The cooling lluid -llowing in tube 1 helps to cool the shaft 2 and falso protect it from the hot fluid exiting through tube 11.

Although FIGURES 1 and 2 illustrate the use of three ceramic arms, it is to be understood that additional arms may be added by one skilled in the art. Likewise, it is possible to employ less than three arms, eg., one arm such as shown in FIGURE 3.

The embodiment of FIGURE 1 can be operated without the use of ballles 9, 9A, and 9B and connecting conduits 10, 10A, and 10B, such that the cooling lluid flow through the supports of each arm is independent of the flow in every other arm. However, when such a system is employed, an unequal pressure drop and temperature regulation results and hot spots can occur with burnout in one or more supports unless the flow conditions in each arm are balanced.

FIGURE 3 represents a modification of FIGURE 1 wherein there is provided only one arm 6 with only one series of supports 3, 4, S, and 8. The lower yor bottom portions of tubes 3, 4, 5, and 3 are not sho-wn in FIGURE 3 but are connected to tubes 1 and 11 the same as illustrated in FIGURE 1. Batlle 9 as shown in FIGUE 1 is removed such that the cooling iluid from support tubes 3, 4, 5, is returned directly to conduit 11 by means of return tube 8.

Since only one arm 6 is provided, the cantilever effect in FIGURE 3 is more pronounced than in FIGURE 1; and accordingly, it may be preferred to uniformly and gradually increase the section modulus of the arm 6 and/or supports 3, 4, 5, and 8 in a direction toward the reactor bottom 12.

Although FIGURES 1, 2, and 3 illustrate the use of four tubes, e.g., 3, 4, 5, 8, it will be obvious to one skilled in the art that fewer 0r more support tubes may be ernployed.

FIGURE 4 represents a further modification. More particularly there is shown three arms 6, 6A, and 6B with ring supports 20 and radial supports 21 connected to a central axial support 11.

In a preferred arrangement, the supports are tubes through which there is circulated a cooling iluid which is from a source (not shown) to axial tube 11. At the top of tube 11 there is shown a further tube 22 with downwardly projecting nozzles 23 from which the circulated iluid is discharged into the interior of the reactor 13.

FIGURES 6 and 7 illustrate a B-dimensional view of a ceramic dedusting arm. More particularly there is shown a ceramic arm 60 having two sides, 61 and 62 at an exterior angle theta 0. Also there is shown side 63 at an interior angle phi p to side 61, such that sides 61 and 63 project to a ceramic dusting edge 64. The broken line 65 represents a tangent to the reactor wall 13 at the projected Contact of the point 64 to the wall, the side 61 being a an angle alpha a to the tangent 65.

FIGURE 8 is a plan view of a modification of the ceramic arm of FIGURE 6. There is shown a ceramic arm having sides 81 and 83 forming a point 84 with an angle phi 6 between the two sides, and a side 82 at an angle theta 0 to the side 81. The broken line 8S represents a tangent to the reactor Wall 13 at the projected contact of the point 84 to the wall 13, the side 81 being at an angle alpha a to the tangent 8S. There is also shown in FIGURE 8 a hole 86 in the body of the arm through which there may be inserted a support rod for the arm. Such a support rod would not have to be resistant to corrosion, e.g., from chlorine and/or oxygen, since the ceramic arm would serve as a protective layer. However, the metal would have to retain a reasonable tensile strength at elevated temperatures, e.g., at about 1,600 F. Such metals would include, for example, alloys of iron, carbon, titanium, zirconium, hafnium, vanadium, tangsten, nickel, and/ or chromium.

FIGURE 9 shows a reactor 92 having an inside wall 93 which is decreased in diameter by means of steps or corbels 94 and 95. As shown in the ligure, there is provided a single ceramic arm 96 which follows the contour of the wall 93.

FIGURE 10 shows a reactor 102 having an inside wall 113 which uniformly and gradually decreases in diameter to a point 117. As shown in the figure, there is provided a single ceramic arm 116 which follows the contour of the wall113.

FIGURE 1l shows the top portion of a reactor 123 having an arrangement of concentric tubes for the introduction of reactants. More particularly, there is shown an inner tube 124 through which an oxygenating gas, e.g., oxygen, NO2, NO3, H203, is introduced into the reactor 123. There is also shown a tube 125 which is concentric to tube 124 whereby an annulus 129 is formed. An inert gas is fed by means of the tube 127 into annulus 129 and then emitted from annulus 129 into the reactor 123. Preferably tube 127 is a wide-angle distribution tube as disclosed in copending U.S. application Ser. No. 360,937, filed Apr. 20, 1964, by Benner and Loehr. By inert gas it is meant any gas which is inert with respect to the metal halide and oxygenating reactants, for example, chlorine, argon, nitrogen, helium, krypton, xenon, carbon dioxide, or mixtures thereof.

External to tube 125, there is provided concentric tube 126 such that annulus 130 is formed. Metal halide, preferably in a vaporous state, is introduced through tube 128 into annulus 130, the halide then flowing into reactor 123. Tube 128 is preferably a wide-angle distribution tube, the same as tube 127.

Where only one ceramic arm is employed, e.g., as disclosed in FIGURES 3, 9, and 10, the arm is characteristically rotated about the inside circumference of the reactor wall at a rate of 1/s to 540 revolutions per hour, preferably 11/2 to 4 revolutions per minute, that is, at a preferred rate of about 80 to 250 feet of internal wall circumference per minute for a rea-ctor 14 feet in diameter. Where more than one arm is used, the rate may be appropriately decreased by a factor equal to the total number of ceramic arms employed.

As noted hereinbefore, it is essential that the dedusting arm be of a ceramic material since other materials, particularly metals, wear quickly and cause the dedusting arm to become a compaction device and bend inwardly. Any ceramic material may be employed which has a thermal conductivity of less than 210 B.t.u./(hr.), (sq. ft.), F./ inch), preferably less than 25, and a hardness of at least 5.0 on the Mohs Scale (where talc equals 1.0 and diamond equals 10.0). In addition the ceramic should have sufficient resistance to a corrosive environment, e.g., chlorine, at an elevated temperature of 1,832" F.

A typical ceramic which is used in the practice of this invention is a steatite product of talc such as Likewise, there may be used ceramic materials containing fused oxides such as alumina (A1203), zirconia (ZrOg), thoria (T1102), beryllia (BeO), rnagnesia (MgO), apinel (MgAl2O3), forsterite (Mg2Si04); also ceramic nitrides such as silicon nitride, aluminum nitride, boron nitride; ferroelectric ceramics such as barium titanate; or mixtures of same. Likewise, silicates, e.g., aluminum silicate or magnesium silicate may be used. In additionthere may be employed ceramics containing CaSi03 (wallastonite), Al2(Si2O5)2(OH)2 (pyrophyllite),

(sillimanite), Al6Si2013, and Mg3(Si205)2(0H) as well as mixtures of same.

Typical compositions would include 78 percent by weight A1203 and 2O percent by weight Si02; 81 to 85 percent by weight A1203 and 14 to 16 percent by weight Si02; 70 percent by weight A1203; and 92.5 percent by weight Zr02 and 5 percent by weight CaO; and 97 percent by weight MgO and 2 percent by weight Si02. Furthermore, the ceramic wall of the reactor is preferably selected from the same or similar ceramic and lava materials.

If metal supports are provided as illustrated in FIG- URES 1 to 5, it is desirable that a cooling fluid be circulated internally of the supports in order to keep the surface temperature of the selected support material below the temperature at which the metal material corrodes, e.g., from attack by halides and/ or halogen gases particularly chlorine, and below the temperature at which the metal strength sharply declines. At lower temperatures, the tensile strength of the metal-like materials is greater than at higher temperatures. Where the supports are constructed out of nickel or a nickel alloy, the surface temperature should be maintained below the temperature at which chlorine or other halide will attack the metal, e.g., below 1000 F. for most nickel alloys, preferably 500 to 700 F. The surface temperature of the metal support is preferably controlled by regulating the volume per unit time of cooling fluid which is circulated internally of the support.

Where a support is provided internally of the arm, as illustrated in FIGURE 8, such support may be a solid member since it will be protected from corrosion by the surrounding ceramic arm.

Typical nickel alloys which may be employed are listed in the Handbook of Huntington Alloys, published by the Huntington Alloy Products Division of the International Nickel Company, Inc. (lst edition, March 1962) on pp. 4 and 6, particularly Nickel 200 which consists of 99.45 percent nickel, 0.06 percent carbon, 0.25 percent magnesium, 0.15 percent iron, 0.005 percent sulphur, 0.05 percent silicon, and 0.05 percent copper, all by weight.

The cooling uid employed comprises air, H20 (water or steam), or inert gases such as nitrogen, argon, helium, krypton, xenon, carbon dioxide or mixtures thereof. Furthermore, the reactants, eg., metal halide such as TiCl4 or oxygen-containing gas may be passed internally through the support tubes such that the tubes are cooled and the reactants are preheated. The preheated reactant can then feed direcly into the reaction chamber, e.g., as illustrated in FIGURE 4. Likewise, various liquid and gaseous nucleating or rutile promoting agents may be employed as a cooling heat transfer fluid, particularly those metals which form a white oxide such as silica and alumina. In addition, carbon monoxide maybe circulated as a cooling uid in place of, in addition to, or mixed with the gases noted above, the C0 then being fed into the reaction chamber to be oxidized and to supply heat to the reaction zone for the sustaining of the reaction. Sulphur-containing compounds as disclosed in copending U.S. application Ser. No. 15,300, now U.S. Patent 3,105,742, may also be employed. Finally, the cooling fluid may comprise a recycle stream of gases from the reactor chamber, preferably a recycle stream from which the metal oxide pigment product, e.g., TiO2 has been precipitated or otherwise removed from the effluent gas stream, e.g., by means of a dust collector or cyclone.

The point or edge of the ceramic arm is located and positioned adjacent to the internal surface of the reactor wall at a distance of 1A inch (one-quarter inch) to 9 inches (nine inches) preferably 3A inch (three-quarter inch) to 2 inches (two inches).

The angle u (alpha) as shown in FIGURES 7 and S should exceed (ninety degrees), preferably 110 (one hundred ten degrees) to 145 (one hundred forty-five degrees).

The angle theta as shown in FIGURES 6 and 8 suitably should exceed whereas the angle phi in FIG- URES 6 and 8 suitably should range from 15 to 75 preferably 30 to 55.

Where the scraper arms and supports are projected upwardly from the bottom of the reactor as disclosed in FIGURE 1, there is a cantilever effect such that the portion of the supports near the bottom is under greater stress than that portion at a greater distance from the bottom. This cantilever alfect is particularly pronounced where a single arm (with supports) is employed, e.g., FIGURE 3.

The cooling fluid is introduced into the system, e.g., Via conduit 1 in FIGURE 1, at a temperature of 150 F. to 300 F., preferably 200 F. to 250 F., such that it exits, e.g., conduit 11 in FIGURE 1, at a temperature of 200 F. to 500 F. Temperatures below 150 F, tend to cool the reaction Zone whereas temperatures above 300 F. cause the supports to overheat.

Where the cooling uid is a gas, it suitably is flowed through the supports at 300 to 900 standard cubic feet per minute calculated at 70 F. and one atmosphere (14.7 pounds per square inch absolute) pressure.

Where air is employed as a cooling media in the practice of this invention, it has been found that the optimum air ow rate (standard cubic feet per minute) per effective outside cooling area of the metal supports (square feet) should range from to 10, preferably 6.5 to 8.5. Effective outside cooling area is defined as that external portion of the support exposed -to the reactor corrosion and thermal conditions, e.g., that portion exposed within the reactor.

Where the length of the arm and supports is long, e.g., in excess of feet, the section modulus of at least one support should be gradually and uniformly increased in a direction toward the reactor bottom in an amount sucient to withstand and endure the increasing stress.

Where a support is a tubular element with an internal diameter d and an outside diameter D, the section modulus Z is determined by the formula:

Where a support has a square cross-sectional area with an outer side A and an internal square opening having a side B, with a uniform wall thickness between A and B, and if the side A is parallel to the reactor tangential at the point of projection of the ceramic arm edge, the section modulus Z is determined by the following formula:

Where the support is an eliptical tube, e.g., conduits 8, 8A, and 8B in FIGURE 1, having an outer major radius a, outer minor radius b, inner major radius c, minor radius d, the section modulus is determined by the following formula:

@i3d-63d Z- 0.7854 T In the practice of this invention, it has been found particularly advantageous to employ a vapor phase oxidation process wherein aluminum trichloride (AlCl3) is added as a nucleating agent to the reaction zone, preferably with the metal halide reactant, c g., TiCl4, in an amount sufficient to give a nal TiO2 pigment product containing 0.1 to 8 percent A1203, preferably 1 to 4 percent by Weight 0f the pigment.

When so practicing the invention, the Ti02 pigment which adheres to the reactor Wall surprisingly contains a higher percent by weight of A1203 than the Ti02 product exiting from the reactor. Thus, whereas the product contains 11/2 percent by weight A1203, the TiO2 on the wall surface contains 3 to 7 percent, usually about 5 percent, by weight A1203.

The following are typical Working examples.

EXAMPLE I Three ceramic dedusting arms were arranged in a vertical cylindrical reactor as shown in FIGURES 1 and 2. The reactor was 14 feet long with an internal diameter of 4 feet one-sixth (1/6) of the internal wall was constructed out of brick comprising 45.1 percent A1203, 51.9 percent Si02, 1.4 percent Fe203, 1.7 percent T102, 0.1 percent CaO, 0.3 percent Na20, and a trace of MgO, all by weight and the remaining tive-sixth was constructed out of brick comprising 40.0 percent A1203, 54.6 percent Si02, 2.4 percent Fe203, 1.2 percent Ti02, 1.5 percent CaO, 0.1 percent MgO, 0.4 percent alkalies, all by weight.

All of the supports for the ceramic arms were constructed out of a Nickel 200 consisting of 99.45 percent nickel, 0.06 percent carbon, 0.25 percent magnesium, 0.15 percent iron, 0.005 percent sulphur, 0.05 percent silicon, and 0.05 percent copper, all by weight.

The supports 4, 5, 4A, 5A, 4B, and 5B were fabricated out of 1 inch .,Slldllls 40 pipe flattened into an ellipse having a major outside axis or diameter of 11/2 inches (one and one-half inches).

The supports 8, 8A, and 8B were fabricated out of 3 inch Schedule 40 pipe flattened into an ellipse having a minor inside axis or diameter 1%6 inches (one and ninesixteenths inches.)

The supports 3, 3A, and 3B were fabricated out of 2 inch Schedule 40 pipe flattened into an ellipse having a minor inside axis or diameter of about 11/2 inches (one and one-half inches).

Exit conduit 11 was fabricated out of 8 inch Schedule 40 pipe.

Inlet conduit 1 was fabricated out of 6 inch Schedule 40 pipe.

Tubes 10, 10A, and 10B were fabricated out of 11/2 inch Schedule 40 pipe.

Shaft 2 was fabricated out of a 3 inch hot rolled carbon steel and was connected to a 7.5y horsepower motor by means of a belt drive, the motor being designed to rotate the shaft 2 and the ceramic arms at 3 revolutions per minute.

The ceramic arms 6, 6A, and 6B were constructed out of a steatite product of talc, 3Mg04Si02H2O. Angles theta and phi were respectively about 135 (one hundred thirty-five degrees) and 30 (thirty degrees). Angle alpha was in excess of (ninety degrees).

At the top of the reactor three concentric tubes were arranged as shown in FIGURE l1, 38 gram-moles per minute of oxygen at 1,150 C. being continuously fed through tube 124 having an internal diameter of 4 inches while 32 gram-moles per minute of titanium tetrachloride at 525 C. was continuously fed through tube 128 into annulus 130 having a maximum diameter of 12 inches. Chlorine at 400 C. was continuously fed at a rate of 5 to 7 gram-moles per minute into annulus 129 having a maximum diameter of 7 inches.

Sixty to 130 grams per minute of vaporous aluminum trichloride at 300 C. were introduced into the TiCl4 stream before it was fed into annulus 130. Liquid silicon tetrachloride at the rate of 0.19 gram-moles per minute was also added to the TiCl4 before the introduction of the TiCl4 into the annulus.

As the three ceramic arms were rotated at three revolutions per minute along the internal wall surface of the reactor, air was circulated by blower means through the supports at the rate of 550 standard cubic feet per minute calculated at 70 F. and 1 atmosphere (14.7 pounds per square inch absolute). The air was fed into conduit 1 at 225 F. and 13.5 pounds per square inch gauge. The exit temperature of the air stream to the atmosphere from conduit 11 was 375 F. the pressure drop of the air stream through the system being 13.5 pounds per square inch.

The design air velocity through each support 4, 5, 4A, SA, 4B, and 5B was 129 feet per second. The design air velocity through each support 8, 8A, 8B was 113 feet per second. The calculated air flow rate per effective cooling area of the supports was 7.85 standard `cubic feet of air at 70 F. and one atmosphere per square foot of effective external cooling area for the supports.

The process was operated continuously in excess of 168 hours and intermittently in excess of 1,440 hours without any plugging of the reactor. During this time, the metal oxide removed from the reactor walls analyzed at 3 to 6 percent by weight A1203. By comparison, the pigmentary T102 product exiting from or near the reactor bottom contained 3%: to 2 percent by weight A1203.

The product was then wet finished and coated with 0.01 to 8 percent by weight silica, 0.1 to 4 percent by Weight Ti02, and 0.05 to 15 percent by weight A1203, (all basis the weight of the pigment) in an acid pH media using the procedure set forth in the copending U.S. application Ser. No. 121,327 filed luly 3, 1961, by Dr. Hartien S. Ritter, now U.S. Letters Patent 3,146,119.

A typical pigment product after wet coating had a tinting strength in excess of 1720 on the Reynolds Scale as 9 determined in accordance with ASTM D-332-26, 1949 Book of ASTM Standards, part 4, p. 31, published by the American Society For Testing Materials, Philadelphia 3, Penn.

EXAMPLE II The procedure as set forth in Example I was followed except that the ceramic arms and nickel supports were removed from the reactor. In other words, the vapor phase TiOZ oxidation was operated not in accordance rwith this invention.

The reactor was operated continuously for 24 hours at /Which time Ti02 buildup on the internal surface of the reactor plugged the reactor. A typical pigment product after wet coating had a tinting strength on the Reynolds Scale below 1,650.

EXAMPLE III The procedure as set forth in Example I was followed except that no ceramic arms were employed. Instead a rotating air-cooled nickel alloy edge was used. The ydevice was operated intermittently for 192 hours out of 360 hours at which time it structurally failed due to abrasion and heat stress. In addition the nickel edge tended to compact lthe metal oxide onto the surface of the wall and did not satisfactorily remove it.

Although this invention has ybeen described witlh particular reference to titanium tetrahalide, eg., TiCl4, TiBrr, and TiI4, it may be used in the production of other pigmentary metal oxides.

The term metal as employed herein is defined as including those elements exhibiting metal-like properties, including the metalloids. Examples, not lbfy wary of limitation but by way of illustration, of pigmentary metal oxides which may be produced by the aforementioned process are the oxides of aluminum, arsenic, beryllium, boron, gadolinium, germanium, hafnium, lanthlanum, iron, plhosphorus, samarium, scandium, silicon, strontium, tantalum, tellurium, terbium, thorium, thulium, tin, titanium, yttrium, ytterbium, zinc, zirconium, niobium., galliuim, antimony, lead, and mercury.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings, 'and Iwill lbe obvious to one skilled in the art. Thus, it will lbe understood that the invention is in no Way to be limited except as set forth in the following claims.

I claim:

1. A method for removing metal oxide formed from oxidation of metal halide from the internal surface of a reactor, which comprises passing a solid ceramic edge having a s-ufciently thigh resistance to a corrosive environment, a thermal conductivity of less than 210 B.t.u./ (hour), (square foot), F./ inch) and a Mohs hardness of lat least 5 in 4displacing contact with the metal oxide but spaced from the reactor surface over the metal oxide.

2. A method according to claim 1 wherein the ceramic edge is an aluminum silicate.

3. A method according to claim 1 wherein the ceramic edge is spaced from 0.25 to 9 inches from tlhe reactor surface.

4. A metho'd according to claim 1 |wherein the ceramic edge is a material [having the composition alpha and phi, as shown in FIGURE 7, are respectively greater than 90 and Within the range of 15 to 75.

6. A method according to claim 5 Iwherein angle alpha ranges from 110 to 145.

7. A method for removing metal oxide accumulation from the internal surface of a metal halide vapor phase oxidation reactor, which comprises passing a solid ceramic edge having a suciently Ihigh resistance to a corrosive environmnet, a thermal conductivity of less than 210 B.t.u./ (hour), (square foot), F./inch) and a Moths hardness of at laest 5 over and in 'dislodging contact with the Imetal oxi'de accumulation but spaced from the internal surface of the reactor.

8. A metihod of removing metal oxide `dust formed from oxidation of metal halide from the internal wall of a cylindrical reaction chamber, which comprises moving a solid ceramic edge having a suiiicien'tly high resistance to a corrosive environment, a thermal conductivity of less than 210 Btu/(hour), (square foot), F./inch) and a Mohs hardness of at least 5 in contact with and over the metal oxide and in a circular pathy concentric to but spaced from the internal wall of the reaction chamber.

9. A method for dislodging metal oxide accumulation formed from oxidation of metal halide that is deposited on the Wall of a reactor, which comprises continuously passing at least one solid ceramic edge having the composition 3MgO'4SiO2-H2O in dislodging contact with and over the surface of the accumulation.

10. A method for dislo'dging metal oxide accumulation from the internal 'wall of a cylindrical metal halide vapor phase oxidation chamber, whiclh comprises passing at least one solid ceramic edge having a sufficiently high resistance to a corrosive environment, a thermal conductivity of less than 2l() B.t.u./ (hour), (square foot), F./inch) and a Mohs hardness of at least 5 over the surface of and in dislodging contact `with the metal oxide accumulation and in a circular path concentric to but spaced from the Wall of the chamber.

11. A method according to claim 10 wherein the solid ceramic edge is spaced a distance of from 0.75 to 2 inches from the wall of the chamber.

12. A method according to claim 10 wherein the ceramic edge is a steatite product of talc.

13. A method according to claim 10 wherein the angles alpha and phi, as s-hown in FIGURE 7, range respectively from 110 to 145, and from 15 to 75.

14. A method according to claim 10 vvhcrein the angles alpha, theta, and phi, las shown in FIGURE 7, respectively exceed l", exceed 135, and range from 15 to 75.

1S. A method for dislodging metal oxide accumulation from the internal wall of a cylindrical metal halide vapor plhase oxidation chamber, which comprises passing an aluminum silicate ceramic edge over the surface of and in 4dislodging contact with the metal oxide accumulation and in a circular path concentric to but spaced from the wall of tihe chamber.

References Cited UNITED STATES PATENTS 9/ 1957 Schaumann 23-202 NORMAN YUDKOFF, Primary Examiner.

EUGENE P. HINES, Assistant Examiner.

U.S. Cl. X.R. 

